Via USA Today:
Several tech companies including Netflix and Digg are participating in a digital protest supporting net neutrality. The protest is part of Internet Slowdown Day, targeting cable companies that supporters of the movement say want to slow down the Web. Now, this won’t mean sites will intentionally slow their services to make this point. Instead, visitors to sites like Netflix, Digg, Reddit, Mozilla, Etsy and Foursquare will display messaging with the iconic, spinning “loading” symbol. They will also urge users to share their complaints with the Federal Communications Commission and Congress. Several apps may also display prompts to stop cable companies’ “slowlane.”
Here’s a great explanation of the issue.